Optical communications networks are becoming more and more prevalent. This is because they facilitate high bandwidth long haul connections among nodes in a data network. All “optical networks” currently operating, whether commercially or merely for research purposes, transmit data signals which in actuality are converted from the optical to the electrical domains at some point in the routing, switching, processing or transmission of the data signals. The more that the data signals can be routed, switched, processed and transmitted in the optical domain, the better the overall benefit to system efficiency in terms of conversion losses and throughput potential. Thus the future looms brightly for all optical data networks.
In order to accurately monitor and maintain system performance, such a system must have a means of measuring and monitoring the optical signals managed by it. The system must regularly monitor certain performance parameters of the optical signals to determine overall signal strength, and the information content of these signals. As well, since many optical data network topologies utilize redundancy as a fail-safe and backup strategy, the optical signal is often monitored at the input and output ports of various system components and used as a means to choose which of two redundant components will carry the actual signal.
In light of the above discussion, the Optical Power (OP) and the Optical Signal to Noise Ratio (OSNR) of a given service wavelength are two key Optical Performance Monitoring (OPM) parameters that need to be measured in optical networks. These measurements facilitate service maintenance as well as fault isolation in optical networks.
In order to increase the data traffic that can be carried on a given physical fiber, modern optical communications systems utilize Dense Wave Division Multiplexing, or DWDM. This is a technique whereby many different optical wavelengths, each carrying its own signal, are combined for transport, and are demultiplexed at network nodes for routing and other processing. DWDM has thus become a mainstay technology for multiplying the available bandwidth in optical systems. Current optical communications systems measure the OP and OSNR on the multiplexed signal. This method, which must acquire information from a band-wide signal (such as the currently utilized 1529 nm to 1562 nm wavelength range) takes time. As well, current OPM devices also use discrete components, and, as a result, the overall device sizes range in centimeters or inches. This size is cumbersome. Further, these OPM devices are incapable of integration with other network nodal circuitry on one chip or substrate, and the results of optical performance measurement are not as immediately available to the control circuitry as they could be if the signal was merely being sent from one part of an integrated device to another.
Additionally, the present embodiments of such measurement schemes are slow in speed (typically 100 msec to 2 sec scan time) relative to the data rates. Thus, if failure detection is dependent upon optical performance measurement, much data will be lost before a failure can even be detected. As data rates continue to migrate higher, this effect becomes more and more pronounced. For example, at the OC-768 data rate of 40 Gb/s, 5 Megabytes of data are lost before the failure can even be detected.
What is thus needed is an optical performance measurement device with increased acquisition speed and greater compactness, allowing a more efficient optical characterization of DWDM signals.
What is further needed is an optical performance measurement device that is small enough to be integrated with other network circuitry, thus increasing the speed of availability of performance information to decision and monitoring circuitry, as well as allowing the fuller integration and miniaturization of optical network node functionalities.